1. Field of the Invention
The present invention relates to electrical connectors and more particularly to electrical connectors which are used for miniaturized, high density and high pin count applications.
2. Brief Description of Prior Developments
Recent advances in the design of portable or mobile electronic equipment have required that connector technology keep pace with the trends of miniaturization and functional complexity. Connectors used in such applications need to be more substantially densely packaged than was heretofore generally required. Such board to board types of connectors are usually used to interconnect two printed circuit boards in an "mezzanine" configuration. Such uses require connectors not only with smaller contact pitches, but, in some cases, with lower mating heights, as well. The resulting increased packaging density must ordinarily be achieved without significant sacrifice of mechanical ruggedness since such connectors may be subjected to unusually high stresses because of the nature of the application. For example, miniaturized or mobile type products are subject to high stresses if they are dropped or otherwise abused. Such high stresses have the potential for damaging connector housings, contacts and solder joints. Furthermore, the connectors themselves might separate if sufficient retention forces are not available.
The "blade-on-beam" connector design is commonly used for miniaturized designs of 0.8 mm and less. This design typically uses a single cantilever beam type of contact for the spring contact which mates an associated blade contact, which does not have spring characteristics. The contact beams generally can be of two configurations.
One such configuration is an edge stamped or "tuning fork" configuration in which the contact is blanked from flat material and reoriented 90 degrees when it is inserted into the housing so that the blanked edge of the beam is in contact with the blade. This design has the advantage that complex configurations which have a high degree of compliance can be easily stamped. The cantilever beam geometry can also be optimized by stamping an idealized shape into the profile of the beam. For example, a constant stress beam with a parabolic shaped thickness profile might be readily stamped. This approach might allow for lower contact height and tighter pitch contacts. The mounting of the contact in the housing is generally accomplished by individually stitching the contacts into the housings.
An alternative design makes use of a more conventional approach in which the beam is stamped so that the rolled edge of the material is in contact with the blade. In this case the contacts can usually be stamped on the same pitch as the final configuration, and the forms of the contact are created by bending the material during the die stamping operation. Although these beams are usually not quite as mechanically efficient as the edge stamped design, they often are more cost effective since they can be mass inserted or insert molded into the housing thus making assembly either easier or less costly from either a product or machine standpoint. This type of product is also easier to electroplate and the contact surface is usually superior to the edge stamped type of contact.
The design of connectors with a contact pitch of less than 1 mm and with mating height of less than 5 mm often presents particularly difficult design problems. The small pitch of the contacts require tightly controlled tolerance on the pitch to prevent shorts. This requirement for precision and accuracy extends to the contact forms and housing geometry's as well. This design process is further complicated by the high internal stress generated by the contact beams themselves, which can generate distortions of the housings and result in reduced contact forces over a period of time, particularly at elevated temperatures. If these connectors are to be manufactured reliably, unique manufacturing methods are required, which can assure the dimensional accuracy as well as physical strength of the product within the dimensional constraints of the product requirements.
There is, therefore, a need for an electrical connector that is not only denser, smaller, but is mechanically rugged. This all needs to be accomplished in the context of lowered manufacturing costs. Some of the specific requirements for this class of connectors may be that contact pitch is from 0.8-0.5 mm, mating height is from 8 mm-3 mm, connector width is from 6-7 mm and pin count of from 10 pos-200 pos.